Tiffany is 2 times as old as Stephanie. 35 years ago, Tiffany was 9 times as old as Stephanie. How old is Stephanie now?
Explanation: We can use the given information to write down two equations that describe the ages of Tiffany and Stephanie. Let Tiffany's current age be $t$ and Stephanie's current age be $s$ The information in the first sentence can be expressed in the following equation: $t = 2s$ 35 years ago, Tiffany was $t - 35$ years old, and Stephanie was $s - 35$ years old. The information in the second sentence can be expressed in the following equation: $t - 35 = 9(s - 35)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $s$ , it might be easiest to use our first equation for $t$ and substitute it into our second equation. Our first equation is: $t = 2s$ . Substituting this into our second equation, we get: $2s$ $-$ $35 = 9(s - 35)$ which combines the information about $s$ from both of our original equations. Simplifying the right side of this equation, we get: $2 s - 35 = 9 s - 315$ Solving for $s$ , we get: $7 s = 280.$ $s = 40$.